1. Field of the Invention
The present invention relates to a stator for an automotive alternator and a method of manufacture therefor.
2. Description of the Related Art
FIG. 9 is a cross-section showing an example of a conventional automotive alternator.
In the figure, bearings 21, 22 are disposed in an aluminum front bracket 1 and an aluminum rear bracket 2, and a shaft 6 having a pulley 4 secured to one end thereof is supported by the bearings 21, 22 so as to be able to rotate freely. A rotor 7 comprising a rotor coil 13 composed of field windings and rotor cores 14 comprising a pair of Lundell-type field cores, is fitted over the shaft 6. Fans 5 are secured to both end surfaces of the rotor 7. Slip rings 9 for supplying an electric current to the rotor 7 are disposed at the other end of the shaft 6 from the pulley 4. A brush holder 11 the rear bracket 2 in a position facing the slip rings 9. A regulator 18 for adjusting the magnitude of the alternating current generated in a stator 80 held between the front bracket 1 and the rear bracket 2 is secured to the brush holder 11. A regulator heat sink 17 being a cooling plate for promoting the cooling of the regulator 18 is disposed on the regulator 18.
A rectifier 12 electrically connected to the stator 80 for converting the alternating current generated in the stator 80 to a direct current is secured to the rear bracket 2. A rectifier heat sink 15 being a cooling plate for promoting the cooling of the rectifier 12 is secured to the rectifier 12.
An electric current is passed through the rotor coil 13 generating a magnetic flux in the rotor 7, whereby magnetic poles are formed in the rotor cores 14. The stator 80 surrounding the rotor 7 comprises: a stator core 81; and a stator coil 82 comprising stator windings composed of copper wire wound around the stator core 81 in which an alternating current is generated by changes in the magnetic flux from the rotor coil 13 as the rotor 7 rotates.
In an automotive alternator constructed in this manner, a current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor coil 13, generating a magnetic flux in the rotor 7. At the same time, since the pulley 4 is driven by the engine and the rotor 7 is rotated by the shaft 6, a rotating magnetic field is imparted to the stator coil 82 and electromotive force is generated in the stator coil 82. This alternating electromotive force is converted to a direct current by means of the rectifier 12, its magnitude is regulated by the regulator 18, and the battery is recharged.
The rotor coil 13, the stator coil 82, the rectifier 12, and the regulator 18 constantly generate heat. Openings are disposed in the front bracket 1 and in the rear bracket 2 to allow an air flow generated by the fans 5 disposed on the rotor 7 to pass through in order to allow the heat generated by power generation to escape. As indicated by the arrows in FIG. 9, cooling air sucked longitudinally from outside the front bracket 1 passes between the air intake ribs 23 and is deflected radially outwards by one of the fans 5. The cooling air cools the front bracket 1 side of coil end portions 82b of the stator coil 82 projecting from the stator core 81, passes between the air return ribs 24 and is discharged to the outside.
Cooling air sucked longitudinally from outside the rear bracket 2 passes between the air intake ribs 25, passes over the rectifier heat sink 15 or the regulator heat sink 17, is deflected radially outwards by the other fan 5, cools the coil end portions 82b on the rear bracket 2 side, passes between the air return ribs 26 of the rear bracket 2 and is discharged to the outside.
FIG. 10 is a perspective view of the stator 80 of the automotive alternator in FIG. 9. The stator 80 comprises a stator core 81 and a stator coil 82 comprising stator windings secured to the stator core 81, and the method of manufacture thereof will be explained using FIGS. 11 to 13.
As shown in FIG. 11, two strips 89 having protrusions and recesses are formed by punching a thin roll of sheet metal. Each of the strips 89 is wound up from one end into a spiral and each layer of the wound up strip 89 is secured by welding to form a cylindrical stator core 81 having a predetermined thickness as shown in FIG. 12. Slots 81a for inserting the stator coil 82 are formed in inner circumferential portions of the stator core 81.
The stator coil 82 is formed into a cylindrical shape by connecting three phases of stator windings as shown in FIG. 13 and is inserted into the slots 81a in the stator core 81.
FIG. 14 is a structural diagram of the stator 80 given in FIG. 9. In the figure, the stator coil 82 comprises: axially parallel portions 821a being those portions which are substantially parallel to the central axis of the stator coil 82; and bridge portions 821b being circumferential portions connecting the axially parallel portions 821a to each other within each of the three phases of windings. Furthermore, the axially parallel portions 821a comprise: current generating portions 821a1 being those portions disposed within the slots 81a and generating electric current; and projecting parallel portions 821a2 exposed beyond the end surfaces 81b of the slots 81a. 
Consequently, the bridge portions 821b and the projecting parallel portions 821a2 of the axially parallel portions 821a are included in coil ends 82b of the stator coil 82 being the projecting portions exposed beyond the end surfaces 81b of the slots 81a of the stator core 81. The regions W occupied by the coil ends 82b are indicated by the dot-and-dash lines in FIG. 15.
A coil insertion device such as, for example, that described in the Japanese Patent No. 2513351, can be used to insert a stator coil 82 such as this so as to fit inside the slots 81a of the stator core 81. Using this coil insertion device to manufacture the stator 80 shown in FIG. 10, the coil ends at the ends of the stator coil 82 on the side to be inserted into the stator core 81 are bent radially inwards and the stator coil 82 is inserted from the inner circumferential side of the stator core 81 by moving the stator coil 82 in an axial direction by means of a jig. After inserting the stator coil 82 into the slots 81a of the stator core 81, the radially inward-bending coil ends are restored to their original shape.
Now, since an electric current will arise in the stator 80 only in the windings within the slots 81a facing the rotor core 14, the windings in the bridge portions 821b and the projecting parallel portions 821a2 are merely passages for the generated current.
However, when the above coil insertion device is used to insert the stator coil 82 into the slots 81a of the stator core 81, the portions of the stator coil 82 required for bending and the portions required for axial displacement by the jig, etc., are only required during the assembly of the stator 80 and do not contribute to the generation of the electric current in the completed stator 80.
For this reason, since there are excess portions of stator coil such as these in the completed stator 80 which are required only for the assembly of the stator 80, the coil resistance value is not small, which does not help to reduce copper loss due to heat generated by the stator coil 82 as a result of the current flowing through the stator coil 82. Consequently, since the portions of the stator coil 82 not contributing to the generation of electric current are numerous, improvements in the output and efficiency of the automotive alternator are hindered. Moreover, having excess portions of stator coil required only for the assembly of the stator 80 has also made stators 80 of such construction disadvantageous from the viewpoint of cost and weight.
Furthermore, the length of the coil ends 82b is sometimes extended in the axial direction to allow more cooling air expelled from the fans 5 to strike the coil ends 82b. However, in this case the stator coil is enlarged and the amount of heat generated rises with the resulting increase in coil resistance. Furthermore, because the gaps 82c between the wires in the bridge portions 821b of the stator coil 82 and between the bridge portions 821b and the end surfaces 81b of the stator core 81 are larger, heat conductivity between the wires in the bridge portions 821b of the stator coil 82 and between the coil ends 82b and the stator core 81 is not good. Still furthermore, because the cooling air is allowed to strike the coil ends 82b, wind resistance is increased and the amount of cooling air is reduced for the alternator as a whole, leading to reciprocal problems such as poor cooling performance, etc., in other heat generating portions such as the rectifier 12 and the regulator 18.
In addition, when the coil ends 82b are made long, they form raised arches having gaps 82c between the bridge portions 821b and the stator core 81, and since the rigidity of the stator is reduced thereby, the amplitude of vibrations generated by magnetic attraction during power generation increase and electromagnetic noise worsens.
Of these vibrations in the alternator, the component in the direction of the central axis of the stator core causes displacement of the stator coil 82 in the axial direction relative to the stator core 81. That is to say that the stator coil 82 is dislodged relative to the stator core 81 and the stator coil 82 interferes with the stator core 81, resulting in a risk of inferior pressure resistance, layer shorting where the coating on the wire is broken, and shorts, etc., in the stator coil 82.
On the other hand, the trend in recent years towards increasing output in automotive alternators has necessitated the insertion of stator coils into the slots at high density, and when a coil insertion device such as that described in the Japanese Patent No. 2513351 is used to assemble the stator 80, protruding portions 81f being circumferentially extending protrusions are disposed on the ends 81d of the teeth 81c forming the slots 81a, as shown in FIG. 10, so that each portion of the stator coil 82 is not dislodged once inserted into the slots 81a, and therefore the slot openings 81e being the circumferential gaps in the slots 81a for insertion of the stator coil 82 are narrow. Consequently, it is becoming increasingly difficult to insert the cylindrical stator coils 82 into the slots 81a. That is to say that, in such an insertion method, abrasion occurs between the stator core 81 and the windings of the stator coil 82 being moved in the axial direction as they are inserted into the slots 81a, particularly in the vicinity of the slots 81a, damaging the windings of the stator coil 82 and giving rise to inferior pressure resistance, layer shorting, etc.
In order to try to solve this problem, it is possible to minimize the damage to the stator coil 82 due to movement and insertion by the method of manufacture for a stator described in Japanese Patent Laid-Open No. HEI 9103252. However, in this method of manufacture for a stator wherein a stator core is manufactured by laminating rectangular parallelepiped strips of thin sheet metal, when the stator coils are inserted into the slots 81a of the stator core 81, the windings are damaged by the circumferentially protruding portions 81f on the ends 81d of the teeth 81c defining the slots 81a. 
Furthermore, because a magnetic field passes between the stator coil 82 and the facing portions of the rotor core 14, it is also desirable from the viewpoint of power generation performance that the teeth 81c be such that the slot openings 81e are made as small as possible. In addition, depending on the shape of the teeth 81c noise problems may arise due to noise generated by the flow of air in the gaps between the rotating rotor core 14 and the many slot openings 81e. Consequently, the shape of the teeth 81c must be appropriately determined giving consideration to power generation performance, noise reduction, and preventing dislodgment of the stator coils. However, it is necessary to avoid the protruding portions 81f as the stator coil is being inserted into the slots 81a, further imposing restrictions on the shape of the protruding portions 81f. 